For some reason it’s very surprising to me that they use Qemu for their VMs.
It’s not at all unusual - QEMU provides the userland components of KVM. KVM doesn’t itself provide any userland tools for interacting with the kernel components, only libkvm.
I’ve often wondered about their infrastructure myself, always assuming it was some heavy duty OpenStack environment of one kind or another.
Clearly they’re on the higher end of sophistication with how they are using their tools, and it’s rather brilliant to me to learn that under all of it is simple QEMU / libvirt. Inspiring actually. They’re basically using a very well and robustly engineered implementation of what we all have on our standard Linux machines.
I’m guessing OpenStack probably wasn’t mature enough when Digital Ocean was founded (2011)?
But yes, as you say, it’s a lot of tooling and a good UI around the same things that everyone can use (much like Linode, although their UI was relatively clunky and they didn’t offer a rich API for a while). Some interesting notes from Netcraft on their growth.